diff --git a/tests/core/test_mock_signal_backend.py b/tests/core/test_mock_signal_backend.py
index 85e2cfd74..a40faea4e 100644
--- a/tests/core/test_mock_signal_backend.py
+++ b/tests/core/test_mock_signal_backend.py
@@ -135,7 +135,7 @@ async def test_mock_utils_throw_error_if_backend_isnt_mock_signal_backend():
 
     for msg in exc_msgs:
         assert re.match(
-            r"Signal <ophyd_async.core._signal.SignalRW object at [0-9a-z]+> "
+            r"Signal <ophyd_async.core._signal.SignalRW object at [0-9a-zA-Z]+> "
             r"not connected in mock mode",
             msg,
         )